China has been creating artificial islands in the resource-rich South China Sea, causing global concern for the environmental damage taking place. These islands have come at the cost of the health of reef structures in one of the world’s most biologically diverse marine areas. Already nearly complete plans for seven islands were announced in June of 2015, which are now home to ports, radar facilities, airfields, and other support buildings allowing China to bolster its presence in a strategic and resource laden area.

China has used dredgers, which are underwater excavation vessels normally used for harbor maintenance, to pump sediment. The process has destroyed reefs and covered surrounding areas with sand and gravel in efforts to establish stable islands for China’s facilities. This has amounted to widespread damage to the ecosystems of the area, which are some of the most biologically diverse in the world. 500 types of reef building coral make this region their home, compared to a total of 70 types in the Caribbean. Aquatic life in the region has never been fully explored or documented, but projections have estimated that the reefs are home to hundreds of thousands of undiscovered species. Experts have warned that plumes of sediment may wash back into the sea and further damage marine life in the South China Sea.

For their part, Chinese officials have claimed that the islands constitute environmentally friendly development, and that any impact on the reefs would be “limited”. Spokesman of China’s Foreign Ministry claimed that island building projects “strictly follow the principle of conducting green projects and building ecological islands and reefs.”

Controversy over the artificial islands has so far been largely focused on the political and military implications. The Spratly Islands, the island chain in the South China Sea at the heart of these tensions, are claimed in part by six different nations in the region, and are mostly occupied by the Philippines and Vietnam. There is widely assumed to be potential for large oil and gas deposits, but the depth and necessary methods for access are still unknown.

China’s aggressive expansion has not only garnered the attention of countries in the region such as Vietnam and the Philippines, but has become a point of tension with the United States. The White House has sent Navy destroyers to patrol within 12 nautical miles of China’s manmade islands. US Defense Secretary Ashton Carter has accused China of undercutting its own stated policies of international cooperation, and of isolating itself in the process.